Sights of the above defined type can be called red dot sights: the light emitting means, normally a light emitting diode (LED), produces a red dot on the optical element, and by the characteristics of the element this dot is shown to the user of the firearm together with the target, on which the dot is to be placed for obtaining a hit.
Normally, the optical element and the LED are built into a housing with the optical element at one end thereof and a protective window at the other end; in this way a fully enclosed and protected design is obtained, which however has the drawback of being comparatively clumsy and add to height, volume and weight of the firearm.
In certain designs the housing is dispensed with, and the optical element rises from the top of the firearm unprotected and vulnerable, even when the firearm is not in use.